Reduce lock contention in properties of Configuration

The properties field of class Configuration is guard by synchronized, and its type java.util.Property is a sub class of java.util.Hashtable, which methods are all synchronized. These are bad for multithread performance.

The properties field should be replaced by a HashMap<String, String> with a ReentrantReadWriteLock, then all get() related operations can be parallel guard by ReadLock, and set/load operations can be guard by WriteLock. This is better for performance.